Projectors or large-size FPDs (flat panel display) have been commonly used in people's daily study, work and entertainment recently. With the development of science and technology, however, it is difficult for conventional input devices to meet people's demands on human-computer interaction. A laser pen is used to point at a display image for indication in the conventional human-computer interaction, while the pointed display system cannot obtain a position coordinate of an indication point and further cannot implement interactive operation commands. Moreover, only a single laser pen can be used for indication in the general display system, and multi-point interactive operations cannot be achieved simultaneously on one picture.